In short, the company Cray offered Id a discount on a Cray 6400 supercomputer if they would portray Cray products within the game somehow. So Romero planned how to show future Cray supercomputers in-game running the slipgates and other in-game tech, and developed models of the slipgates and teleporters with Cray computers built in.

Then before Id ever received their supercomputer, Silicon Graphics bought Cray and shut down the entire deal. Romero had to rebuild the slipgate models without the supercomputers built in, and built out his "computer room" idea into DM6 as a remnant of his concept plans.